Measles is a childhood infection caused by a virus. Once fairly common, measles can now almost always be prevented with a vaccine, according to Mayo Clinic's website.

However, last year’s 644 cases were the greatest number of cases since measles was eradicated from the U.S. in 2000, according to the CDC.

Minnesota is one of 20 states that allow parents to opt out of vaccinations for their children, according to the National Conference of State Legislators. Parents simply have to write a note to their child's school saying the state's vaccination requirement clashes with their beliefs.

A total of 1,959 parents filed objections against the vaccine for measles, mumps, and rubella during the 2013-14 school year, according to the Minnesota Department of Health. While that number reflects only about 2.8 percent of all kindergarten parents, it's more than three times the total of a decade ago.

The growing number of parents choosing not to use the MMR vaccine is connected to misinformation about potential links to autism, according to health experts.

"Over the last two decades, extensive research has asked whether there is any link between childhood vaccinations and autism,” says Rob Ring, the chief science officer of Autism Speaks. “The results of this research are clear: Vaccines do not cause autism. We urge that all children be fully vaccinated."

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A recent analysis of data by the Star Tribune shows a wide range of vaccination rates among Rochester elementary schools. Here are the five local schools that had the highest percentage of unvaccinated (MMR) kindergartners during the 2013-14 school year:

Schaeffer Academy* - 19%

Montessori at Franklin - 8.3%

Rochester Central Lutheran* - 7.9%

Churchill Elementary - 6%

Jefferson Elementary - 5.2%

*Private school

Click here to learn more about how to protect your child from the measles.